Many optical devices can now be integrated on-chip, providing analogous benefits to those
seen with
the shift to electrical integration. However, integrated optical waveguides remain very lossy
compared to their discrete component equivalent, optical fiber. This shortcoming presents a barrier
to the introduction of integrated photonic delay lines with delay times on the order of hundreds of
nanoseconds or more. DARPA has created the Integrated Photonic Delay (iPhoD) program to promote the
development of integrated waveguides that are competitive with optical fiber in propagation loss. By
replacing fiber, these waveguides will reduce the size and weight of devices requiring long delay
lines, as well as allow greater precision in specifying the amount of time delay. Our approach to
this challenge is to eschew traditional integrated waveguides made of materials such as silica, and
instead develop on-chip hollow waveguides with an air core and highly reflective wall surfaces.
Confining the optical power in an air core avoids the problem of bulk losses due to imperfections in
the grown or deposited materials traditionally used for integrated waveguide fabrication.